And do they have a special weapons or something different?
They have a special "clown" mask with a ND paw on it. They also have special Naughty Dog skins for their weapons and a shirt with ND paw.
Anybody with the clan tags of [ND] or [NDI] are Naughty Dog Employees. Yes, anybody can put them as their clan tags, but nobody would be disrespectful enough to use them without being an ND employee.
fadi... lol. Just lol.